Freeze frames take it completely out of context as you have to look how the players got into that position.
Watching the clips on you tube I can eye how people come to the conclusion there was a bite. In reality the video doesn't prove anything except Wellens lead with the elbow into MM's face.
It he was bitten as Wellens seems to claim there will be a bite mark on his arm to show the ref which will be in his report and he will be charged. If he didn't here won't be any marks and he won't be charged. We will have to wait until Tuesday to find out.